Oil recovery process using an unhydrolyzed polyacrylamide and partially hydrolyzed polyacrylamide mobility control agent

ABSTRACT

A mixture of unhydrolyzed polyacrylamide together with partially hydrolyzed polyacrylamide is used for recovery of petroleum. The partially hydrolyzed material reduces permeability and the unhydrolyzed material maintains viscosity.

ilnited States Patent Norton et al. July 3, 1973 1 OIL RECOVERY PROCESS USING AN [56] References Cited UNHYDROLYZED POLYACRYLAMIDE AND UNITED STATES PATENTS PARTlALLY "YDRQLYZED 2.827.964 3/!958 Sandiford et 8]. 166/275 POLYACRYLAMIDE MOBILITY CONTROL 3.039.529 6/1962 McKennon 166/275 AGENT 3.343.60l 9ll967 Pye l66/275 X 3.476.186 ll I969 S I66 275 X [751 lmemmsl Charles David Falk, 3.543.855 121970 I66275 x both f Den r. C l 3.634.305 1/1972 Johnson et al l66/275 x [73] Assignee: Marathon Oil Company, Findlay,

Ohio Primary Examiner-Stephen .l. Novosad Attorney-Joseph C. Herring, Richard C. Willson, 221 Filed: July 19, 1971 Jr et aL 211 Appl. N6; 163,642

[57] ABSTRACT [52] U S 166/275 252/8 55 D A mixture of unhydrolyzed polyacrylamide together [51] Int Cl I n 43/22 with partially hydrolyzed polyacrylamide is used for re- [58] mead 01'55x21:1111111111111111111'1367573 274 275 01mm The Partially hydro/wed were l66/305 R; 252/855 D reduces permeability and the unhydrolyzed material maintains viscosity.

6 Claims, Drawing Figures A 50 50 BLEND OF UNHYDROLYZED POLYACRYLAMIDE (FA) DOW 7OO PARTIALLY HYDROLYZED COMPARED TO DOW 7OO ALONE.

A 7., now 700 75 94, PA

% DOW 70o Moova DOW 70o k IOOX PA RESlDUAL OIL RECOVERY IN SUPPLEMENTED RECOVERY PPM (THICKENER) PATENTED JUL 3 I975 SHEEI IN 5 A 50 5 0 BLEND OF UNHYDROLYZED POLYACRYLAMIDE (PA) DOW 700 PARTIALLY HYDROLYZED COMPARED TO DOW 700 ALONE.

0 O 7 WA DP m 55 Y. 27 O m A A V w 7 z W o D B Va m I A 0 O. 7 W 0A DP 00 w w w m w a w o 200 PPM (THICKENER) 0 FA L K ATTOR PAIENIEIIJULB ms 3.743.018

sum 2 or 5 A SMALL AMOUNT OF UNHYDROLYZED POLYACRYLAMIDE (PA) GREATLY IMPROVES THE OIL RECOVERY WITH DOW 700 PARTIALLY HYDROLYZED POLYACRYLAMIDE.

SYNERGISM G V. RESIDUAL OIL RECOVERED IN SUPPLEMENT RECOVERY m O 25 5O 75 I00 PA I00 75 5O 25 O DOW 700 THICKENER COMPOSITION, WT.

AT 500 PPM TOTAL THICKENER CONCENTRATION F/G. Z

W/TNESSES INVENTORS Z (J71. MMO CHARLES J. NORTON Z 31 D v10 0. FALK PATENIEDJULB ms SHEETBNS BLENO OF UNHYDROLY ZED AND PARTIALLY HYDROLYZED POLYACRYLAMIDE GIVES SUPERIOR OIL PRODUCTION.

O: U 6 U 100 .L M (Z O U 5.. 2 LL! 2 5 75 25%DOW 700 WITH ANAVERAGE a. f 75% PA ass/: 5; 0F 3 HYDROJS/S 0F5% z IMPROVEMENT O V a? so uJ DOW 700 g PARTIALLY HYDROLYZEE f 3 (5.4%.) POLYACRYLAMIDE (PA) 0: o PA J D 9 (I) LL] 0! O 5 I0 I55 20 PERCENT HYDROLYZED w/ TNESSES INVENTORS CHARLES J. NORTON DAVID O. FALK ATTOR Y PATENTEDJUL3 191s 3.743.018

saw u or 5 4 FT. x 3 IN. BEREA (FIRED 825 F) (EXAMPLE 8) 0.03 PV SURFACTANT SLUG /0.s3 PV PHPA 5.42 HYDROLYZED (500 PPM).

[0.0 q i j 7.5 0 I A \rwfl g 5.0 l fi/O E ME :2 fL N u o 2.5 u n: & \J, U LU o 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 THROUGHPUT, PORE VOLUMES A: FRONT PRESSURE TAP u= MIDDLE PRESSURE TAP F/G. 4. 0= REAR PRESSURE TAP W/TNESSES Y INVENTORS EWM. 1% CZCIIELEOS ILJANKORTON M W 1 ATTORN PAIENIEUJM ms 3.743.018

' SHEEI s or 5 4 FT. X 3 IN. BEREA (FIRED 825 F) (EXAMPLE 9) 0.03 PV SURFACTANT SLUG /O.82 PV 25% DOW 70o 75% PA (500 PPM).

' l2 1 t CO g a i 7\ 8 & .5 m m E U LL] o THROUGHPUT, PORE VOLUMES A mom PRESSURE TAP U= MIDDLE PRESSURE TAP F/G. .5. O REAR PRESSURE TAP WITNESSES INVENTORS KW fir. chm CHARLES J. NORTON OIL RECOVERY PROCESS USING AN UNIIYDROLYZED POLYACRYLAMIDE AND PARTIALLY I-IYDROLYZED POLYACRYLAMIDE MOBILITY CONTROL AGENT CROSS REFERENCE TO RELATED APPLICATIONS Ser. No. 85,064 filed Oct. 29, 1970, now US. Pat. No.

3,684,014; Ser. No. 126731 filed Mar. 22, 1971; Ser. No. 133060 filed Apr. 12, 1971; Ser. No. 140931 filed May 6, 1971; and Ser. No. 209,479, filed Nov. 26, 1971.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates primarily to wells classified in Class 166 of the United States Patent Office, and more particularly to production of earth fluid by driving fluid classified in Class 166 subclass 252.

2. Description of the Prior Art Water flooding with mobility-reducing agents, e.g., high molecular weight partially hydrolyzed polyacrylamides, has been successfully used to recover increased amounts of oil in secondary recovery methods. U. S. Pat. No. 2,827,964, teaches secondary recovery of petroleum from subterranean formations using watersoluble partially hydrolyzed acrylamide polymer. U. S. Pat. application Ser. No. 76,140, filed Sept. 28, 1970, copending, teaches improved mobility control of petroleum recovery by injecting at least two slugs, one containing a permeability reduction agent, e.g., partially hydrolyzed, high molecular weight polyacrylamide, and the other slug containing a fluid viscosity increasing agent, e.g., a linear polysaccharide or other biopolymer. Also, U. S. Pat. application, Ser. No. 85,064 filed Oct. 29, 1970, now US. Pat. No. 3,684,014, copending, teaches aqueous slugs containing both polyelectrolyte, e.g., partially hydrolyzed high molecular weight polyacrylamide and nonelectrolyte, e.g., polyethylene oxide, wherein the polyelectrolyte reduces permeability and is gradually depleted as it moves through the formation while the nonelectrolyte increases viscosity and does not undergo such depletion.

U. S. Pat. No. 3,039,529 teaches that the use of unhydrolyzed polyacrylamide is a very expensive operation due to its high absorption characteristics when injected into oil bearing formations.

A design criterion for an optimum flooding process is to have the mobility of the displacing fluid about equal to or less than that of the combination of the formation fluids (hydrocarbon and interstitial water) within the reservoir. As stated above, this has been accomplished by injecting into the water flood a single agent to effect a reduction in mobility. Generally, this agent is a partially hydrolyzed, high molecular weight polyacrylamide.

SUMMARY OF THE INVENTION This invention relates to a method of improving mobility control ofa flooding process by injecting an aqueous solution of unhydrolyzed polyacrylamide and partially hydrolyzed polyacrylamide into the oil bearing formation. The result of the injection of this aqueous solution is a substantial increase in production of petroleum from subterranean formations.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the unexpected synergistic improvement that one obtains with a thickener formulation comprised of 50 percent unhydrolyzed polyacrylamide and 50 percent Dow 700 used to push a 0.03 pore volume of surfactant slug.

FIG. 2 compares the supplemented oil recoveries obtained at various compositions of thickener, all used at 500 ppm concentration. The magnitude of the synergism attained with up to 50 percent Dow 700 with unhydrolyzed polyacrylamide (PA) is indicated by the shaded area between the two curves.

FIG. 3 compares the supplemented oil recoveries obtained with unhydrolyzed polyacrylamide (PA), partially hydrolyzed Dow 700 (20 percent hydrolyzed), another sample of 5.42 percent hydrolyzed polyacrylamide, and a blend of 75 percent PA and 25 Dow 700 with an average degree hydrolysis of about 5 percent. The improved results obtained with the blend of hydrolyzed and unhydrolyzed polyacrylamides indicate bet ter supplemented oil recoveries when the two distinct type of polymers are present rather than one polymer with the same average degree of hydrolysis.

FIGS. 4 and 5 show improved reciprocal mobility control which results in improved oil recovery.

Reciprocal mobility values which are calculated from continuous monitored pressure data at various injections obtained by transducer at the front, middle, and rear of the core are presented for examples 8 and 9. The reciprocal mobility values are calculated by means of the Darcy equation reciprocal mobility KA(AP)/ql where K is the permeability, A the cross-sectional area in C AP the pressure change in atmospheres, q the throughput flow rate in CMlsec, and l is the length of the core.

Comparison of reciprocal mobility data in FIGS. 4 and 5 indicates the improved oil recovery obtained with the synergistic mixture in example 9 is in large part due to the improved reciprocal mobilities sustained throughout the core flood during the supplemented recovery operation, first especially as measured at the front end of the core and later the middle of the core.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Starting Materials By unhydrolyzed polyacrylamide polymer is meant herein high molecular weight polymers containing predominantly acrylamide monomer units.

By partially hydrolyzed polyacrylamide" is meant herein polyacrylamide which has been hydrolyzed to 0.1 to percent, more preferably to 1 to 45 percent, most preferably 5 to 30 percent, of theory.

Partially hydrolyzed polyacrylamide will preferably have molecular weights in the range of from about 0.1 to about 10 X 10, from 0.5 to 6 X 10, and most preferably from 1 X 10 to 5 X 10. Preferably the partially hydrolyzed polyacrylamide will be present in amounts of from about 0.001 to about 10.0, more preferably 3 ,743,018 3 4 from 0.01 to about 1.0, and most preferably from 0.02 EXAMPLES l 9 to about 0.2 weight percent based on the weight of the total solution. The unhydrolyzed polyacrylamide will preferably have molecular weights in the range of from about 0.1 to about 10 X 10 more preferably from 0.5 5

to about 6 X 106, and most preferably from 1 X 106 to Examples 1 through 9 are run under identical condiabout 5 X 10 Prefer ly. the unhydrolyzed p y y tions. The comparabilities of the examples employing amide Will be P1656! in amounts from about 0.001 to various [hickeners in upplemented recovery peraabout 10,1110? Preferably from to about and tions are established by the preliminary data on pore most preferably from 0.02 to about 0.2 weight percent 10 volumes 9v porosities, permeabilities (md), initial based on the tota SOlUIiOH- oil and water saturations (0,, W,) residual oil and water The solvent for the liquid solutions of the present in- Saturations (o d w after preparation i l t d vention were comprised of water, most preferably conwater fl d ith a t i l H n fi ld l nt at d sist essentially of connate water, for example, Palestine il ffi i i f water fl d recovgry (Eff) 11 line water, fresh water, or brackish water. it is prefera- 15 experiments a 3 p m f a petroleum lf t ble that the water contain less than about 300,000, 51 was pushed in the Secondary fl di operamore Preferably less than about 10,000, and most P tion by up to about 1 PV of the particular thickened erably less than about 500 parts per million of dissolved water, I h experiment h i j i f hi k d solids. Th re g aqueous Solution of unhydrolyled water was continued to the point at which no additional l l id nd partially hydrolyzed polyacry oil was recovered. The data are summarized in Table amide will preferably have Viscosity of from about 15 I, the last column of which lists the percent oil recovery to about 1,000 cps, m pref r y from about 5 t0 based on residual oil remaining after the preliminary about 500 cps, and most preferably from 10 to about t r fl d 100 cps.

Examples 1 and 2 establish the reproducibility of this precedure, which together with Experiment 3 give reference data for comparison with a typical partially hydrolyzed polyacrylamide polymer (Dow 700).

While not necessary to the practice of the present invention, various other ingredients including among others, cellulose and surfactants, e.g., polyalkyl aryl sulfonate and other conventional displacement fluid additives may be added to the liquid polymer solutions. Examples 5, and 6 w the u p q synerglsfic preparation f Liquid Systems improvement that one obtains with a thickener formu- It will generally be preferable to merely co-mix the latlon P P of 50 Percent unhydrolyzed P unhydrolyzed polyacrylamide and the partially hydroacrylamlde i P Dow T results are lyzed polyacrylamide and then add water while gently unexpected in light of the art taught in prior patents. stirring to promote dispersion, suspension, and solu- These results are Plotted tion. Bubbling a small amount of non-oxygen gas, e.g., Examples 7, 8, and 9 were carried out to obtain addinatural gas, may be used to effect mild stirring. The intional data on the synergistic behavior of the mixed gredients will preferably be mixed at a room temperathickener system.

TABLE 1 [Summary of thickl-nr-d water supplmnontvrl recoveries lt-rinotr Ex. Run lnrnsllllll y, Il-ruont l'urr-r-nl. No. lnlmln-r lV cc. ity 1nd. 0. W r-ll'. 'lhiuknnr-r l'\/ of t), 10020 1,050 0. .10.: 3.30. X 0. 010 0. 300 415. 4 500 p.[).nl. Dow 700 0. 025 10. 1 02117 1,034 0. 201 357.11 0. 000 0. 301 42. 4 500 11.11.11]. DOW 700 0. 02K 4:"). X 02118 1,008 0. 108 351. 1') 0. 041 0. 350 42. ii 700 ]).]).nl. Dow 700 r 0. .100 52. It 03111 1,017 0. 107 330. l 0. 574 0. 420 37.1 300 p.p.m. :50 lA/DOW 700. 0. 037 43. 0 03112 1, 034 0. 201 388. 4 0.584 0. 410 30. 7 500 11.1).111. 50:50 lA/Dow 700.v 0. 020 48. 1 031121 1, 040 l). 202 386. 2 0.581 0. 410 30. 8 700 p.p.in. 50:50 lA/Dow 700 0. 021 56. 4 11010 1, 071 0. 208 410. ll 0. 013 0. 387 40. .i 500 [1.11.11]. lA 1.051! 27. 7 12010 1,031 0. 100 350. 0 O. 510 0. 481 40. 0 500p.1).1n. llllA (5.42% hydrolyzed) 0. 00. 47. 2 12000 1,054 0. 205 440. 8 0. 524 0. 475 40. 5 500 11.1).m. 25% Dow 700, PA 2 0. 08.1%

1 3 in. diameter by 40.10111: Berea sandstone (fired at 825 F.) was first saturated with llonry plant brine (containing 11,000 p.p.m. Cl, 6,500 p.p.1n. Nuil' flooded to residual saturation (O and W,) and then flood at rates of 1.9 to 3.7 ftJday with [0.03 PV of FF-516 slug (petroleum sulfonate slug) followed by] up to 1 pore volume or synthetic Palestine Water (containing 400 1).p.n1. NaCl and 55 p.p.nr. 011012) and the addition crude recovered and calculated of percent of residual oil in the core before this final flood.

7 interpolated from data. for comparison.

ture somewhat above room temperature, more prefera- Modifications bly from 0C to about C, and most preferably from It will be understood by those skilled in the art that 20C to about 50C. If desired, a mixing operation can the relative proportions of the admixture of unhydrobe employed in one or more full-type mixers or mixing lyzcd polyacrylamide and partially hydrolyzed polytees so long as the proportions of the ingredients are 65 acrylamidcs utilized in the examples herein are merely properly measured and thoroughly mixed. Bacterioexemplary of the relative proportions which may be cides and anti-oxidants can be advantageously added to employed with the present invention. For example, preserve the viscosity of the solution. using nearly 100% "partially hydrolyzed polyacrylamides at the leading edge of the displacement slug and gradually using a higher and higher percentage of unhydrolyzed polyacrylamide to provide a slug which is rich in the depletable component, unhydrolyzed polyacrylamide at its leading edge where depletion is most likely to occur. Initial viscosity of the slug may be the same at all points throughout the slug or may be itself gradually decreased until it approaches that of the drive fluid which displaces the slug through the formation.

What is claimed is:

1. A process for the displacement of oil in an oil bearing formation comprising injecting into said formation an aqueous solution comprised of about 0.001 to about percent by weight of a watersoluble partially hydrolyzed polyacrylamide and about 0.001 to about 10 weight percent water soluble unhydrolyzed polyacryL amide based on the total solution.

2. Processes according to claim 1 wherein the partially hydrolyzed polyacrylamide polymer has a molecular weight above 100,000 prior to comixing with said unhydrolyzed polyacrylamide polymer.

5. Process according to claim 4 wherein the aqueous solution is characterized by a viscosity of from about 5 to about 500 centipoises.

6. Process according to claim 4 wherein the aqueous solution is characterized by a viscosity of from about 10 to about centiposes. 

2. Processes according to claim 1 wherein the partially hydrolyzed polyacrylamide polymer has a molecular weight above 100,000 prior to comixing with said unhydrolyzed polyacrylamide polymer.
 3. Processes according to claim 1 wherein the partially hydrolyzed polyacrylamide has a molecular weight of from about 1, 000,000 to about 10,000,000 and is hydrolyzed to from about 0.1 to about 70 percent of theory.
 4. Process according to claim 1 wherein the aqueous solution is characterized by a viscosity of from about 1.5 to about 1,000 centipoises.
 5. Process according to claim 4 wherein the aqueous solution is characterized by a viscosity of from about 5 to about 500 centipoises.
 6. Process according to claim 4 wherein the aqueous solution is characterized by a viscosity of from about 10 to about 100 centipoises. 